This invention relates to a method and apparatus for measuring the response time of an electrical instrument, and, more particularly to determining the time constant of a thermocouple. The time response of an instrument is the output, expressed as a function of time, resulting from the application of a specified input under specified operating conditions. Response time is the time required for the output to reach a specified percentage of the steady-state or equilibrium value. When the percentage is set at 63.3%, the response time is called one time constant.
One of the most important time responses of an electrical instrument is the step response: the time response of the device when subjected to an instantaneous change in input from one value to another. For example, a thermocouple may be sujected to abrupt changes in temperature. An abrupt change in temperature is tantamount to a step input. In such applications it is essential to know if the thermocouple can respond quickly enough to measure the change. Since the time response of a thermocouple depends on the thermocouple's mass and heat transfer characteristics, it is necessary to calibrate the thermocouple to determine its response time.
Prior art methods of calibrating a thermocouple involve observing the time response of the thermocouple on an oscilloscope or with a printer and then determining the response time of the thermocouple by visual inspection. Such methods are cumbersome and inconvenient to use.
It is therefore an object of the present invention to provide an apparatus for measuring the response time of an electrical instrument.
It is also an object of the present invention to provide a method for measuring the response time of an electrical instrument.
It is another object of the present invention to provide a method and apparatus for measuring the response time of a thermocouple.
Additional objects are set forth in the following description, and in part will become apparent to those skilled in the art upon examination of the following or learned by practicing the invention.